WASHINGTON — President-elect Donald J. Trump moved quickly on Friday to begin filling national security posts at the top echelons of his administration, selecting a group of hawks and campaign loyalists who reflect the hard-line views that defined his run for president.

Mr. Trump said he would nominate as attorney general Senator Jeff Sessions of Alabama, who has been a fierce supporter of a crackdown on undocumented immigrants. The president-elect also moved to install Michael T. Flynn, a retired lieutenant general who has said that Islamist militancy poses a global existential threat, as his national security adviser. And as director of the C.I.A., Mr. Trump selected Representative Mike Pompeo of Kansas, who harshly criticized Hillary Clinton during the House investigation of the 2012 attack on the United States diplomatic compound in Benghazi, Libya.

All three are regarded, in some ways, as outliers from conventional Republican thinking, shunned at times for strident statements, controversial positions or highly partisan moves.

The flurry of announcements indicated that Mr. Trump was gaining control over a transition operation that had been entangled in infighting during its early stages. The results were the first seeds of an administration-in-waiting that will break starkly with that of President Obama.

Transition officials said Mr. Trump would meet over the weekend with a broad array of potential cabinet members and other advisers as a signal that he wanted to build a diverse team, without regard to political affiliation or support for his presidential bid. Among them are Mitt Romney, the 2012 Republican nominee and one of his party’s harshest critics of the president-elect’s campaign, who is a contender for secretary of state, and Michelle A. Rhee, a Democrat who pursued sweeping reforms during her controversy-filled tenure as the District of Columbia’s chancellor of schools.

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Lt. Gen. Michael Flynn, who has been tapped as the national security adviser for the incoming Trump administration, at Trump Tower in Manhattan on Thursday.Credit...Sam Hodgson for The New York Times

Mr. Trump also planned to meet on Saturday with James N. Mattis, a retired Marine Corps general who headed United States Central Command and is being considered for secretary of defense.

But there was no evidence in Friday’s selections that Mr. Trump, who has hinted that he might pursue a more centrist agenda once he sits in the Oval Office, is inclined to moderate his approach on key questions of national security and civil rights.

In a statement on Friday, Mr. Trump called Mr. Sessions a “world-class legal mind,” and added that Mr. Pompeo would be “a brilliant and unrelenting leader for our intelligence community.”

Of General Flynn, he said: “I am pleased that Lieutenant General Michael Flynn will be by my side as we work to defeat radical Islamic terrorism, navigate geopolitical challenges and keep Americans safe at home and abroad.”

Both Mr. Sessions and General Flynn were early and fervent supporters of Mr. Trump’s presidential campaign, even as many establishment Republicans were criticizing Mr. Trump for inflammatory statements and dismissing his chances of winning the nomination. Mr. Pompeo initially supported Senator Marco Rubio of Florida in the Republican primary, but switched after it became clear Mr. Trump would be the nominee. Mr. Pompeo is also close to Vice President-elect Mike Pence, who is heading the transition effort.

In 1986, Mr. Sessions — who, if confirmed, would be charged with safeguarding civil rights in the United States — was blocked from becoming a federal judge by the Senate’s Republican-controlled Judiciary Committee because of previous racially charged comments and actions.

In testimony before the committee, former colleagues said that Mr. Sessions had referred to the N.A.A.C.P., the Southern Christian Leadership Conference and other civil rights groups as “un-American” and “Communist-inspired.” An African-American federal prosecutor, Thomas H. Figures, said at the time that Mr. Sessions had referred to him as “boy,” and testified that Mr. Sessions had said the Ku Klux Klan was fine “until I found out they smoked pot,” a remark Mr. Sessions later dismissed as a joke.

Aides to Mr. Trump dismissed the past statements, and described Mr. Sessions as a champion of civil rights, citing as evidence a number of desegregation lawsuits he filed while serving as a United States attorney in Alabama, his votes to extend the Voting Rights Act and to confirm Eric H. Holder Jr. as the first African-American attorney general, and his efforts to award the Congressional Gold Medal to Rosa Parks.

“Senator Sessions is someone who’s universally respected across party lines in the United States Senate,” said Jason Miller, a spokesman for Mr. Trump’s transition team, calling him “very well qualified for this position.”

Senator Jeff Flake, Republican of Arizona, said on Twitter that Mr. Sessions was “well liked and well regarded, even by those who don’t always agree with him.” He added, “I look forward to supporting his nomination.”

Other Republican senators and conservative groups likewise rallied behind Mr. Sessions, while Democrats have pledged to keep an open mind on confirming him. But, in a reflection of the tough questions he is likely to face in his confirmation hearing, civil rights groups and their champions in Congress condemned the choice.

“Given some of his past statements and his staunch opposition to immigration reform,” said Senator Chuck Schumer of New York, the new minority leader, “I am very concerned about what he would do with the Civil Rights Division at the Department of Justice, and want to hear what he has to say.”

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Representative Mike Pompeo was a harsh critic of Hillary Clinton during hearings by the House Benghazi panel.Credit...Jacquelyn Martin/Associated Press

Mr. Trump’s selection of General Flynn, which does not require Senate confirmation, was similarly cheered by conservative organizations and met with alarm by Democrats. He has called Islam a political ideology that has “metastasized” into a “malignant cancer.” After building a reputation as a respected military officer, he was fired by President Obama after two years as the chief of the Defense Intelligence Agency. General Flynn has since been a vociferous critic of a Washington elite he contends has refused to name radical Islam as the enemy, and is therefore doomed to fall short in defeating it.

“His statements about Muslims are profoundly un-American as well as damaging to the fight against terrorism and national security,” said Senator Ron Wyden, Democrat of Oregon and a member of the Intelligence Committee. “He has indicated an openness to torture and the destruction of an entire city, both of which are clearly illegal, not to mention immoral and destructive to America’s global leadership.”

Mr. Wyden said that the president-elect, who last week chose Stephen K. Bannon, who has promoted hard-right nationalism as the chairman of Breitbart News, appeared to be building “a White House leadership that embodies the most divisive rhetoric of his campaign.”

Mr. Pompeo, a graduate of the United States Military Academy at West Point and Harvard Law School, was elected to Congress in 2010 with substantial financial backing from a political action committee funded by Koch Industries, based in Wichita, Kan. He has criticized Mr. Obama’s decisions to shut down the C.I.A.’s “black site” prisons and to require all interrogators to strictly adhere to anti-torture laws. In 2014, he accused Mr. Obama of refusing “to take the war on radical Islamic terrorism seriously.”

After the House Select Committee on Benghazi found no new evidence of wrongdoing by the Obama administration or Mrs. Clinton, who was the secretary of state at the time of the attack, Mr. Pompeo and another Republican on the committee, Representative Jim Jordan of Ohio, said they were convinced there had been a cover-up, and they filed a 48-page addendum that included far harsher criticism of the administration and of Mrs. Clinton. Other Republicans, including the committee’s chairman, declined to add their names to the document.

“While we have had our share of strong differences — principally on the politicization of the tragedy in Benghazi — I know that he is someone who is willing to listen and engage, both key qualities in a C.I.A. director,” Mr. Schiff said.